Device for the monitoring of ice formation

Abstract

The device contains a first light source (21) that emits a continuous light and a second light source (18) that emits intermittent light, a photodiode (19) that responds to the light of both light sources and a transparent plate (14) that is located in the light path between the first light source and the photodiode and the surface of which constitutes a measuring surface for ice formation. As long as the measuring surface does not ice up and the plate remains optimally transparent, the photodiode is pushed into the area of saturation by the light rays of the first light source and the light rays of the second light source have little influence on the photocurrent. If ice forms on the measuring surface the light rays of the first light source are weakened and the photocurrent of the photocell is increasingly modulated by the light rays from the second light source. The modulated photocurrent is used as a quantitative signal for the build-up of the ice layer. As the formation of ice impairs the transparency of the plate, by experience, much more rapidly than a coating with dust, it is possible to distinguish between an accumulation of dirt and ice formation on the plate with the aid of electronic circuit that monitors the time-related decrease of transparency.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A device for monitoring the formation of ice, comprising: a first radiation source for continuously emitting radiation;   a second radiation source for intermittently emitting radiation;   light-sensitive means disposed so as to receive said radiation from said first and second radiation sources and capable of producing an electrical output signal in response to said radiation from either radiation source;   a transparent element disposed between one of said radiation sources and said light-sensitive means, the transparency of said transparent element being changeable depending upon whether said transparent element is clean or is contaminated with a deposit of foreign material; and   circuitry means responsive to said output signal of said light-sensitive means, said circuitry means providing at least one output for indicating the presence of ice on said transparent element, wherein said output signal of said light-sensitive means varies as a function of said changes in transparency of said transparent element and may be substantially continuous or substantially intermittent depending on the transparency of the transparent element.   
     
     
       2. The device of claim 1, further comprising a case, wherein one of said radiation sources is disposed outside said case, the other radiation source and said light-sensitive means are disposed within said case, and said transparent element is disposed in an opening in a wall of said case. 
     
     
       3. A device according to claim 1 wherein the light sensitive means shows a characteristic curve for the output signal depending on the incident rays with a steep, almost linear part in the area of lesser incident rays and, in the area of stronger incident rays, a flattening part, changing into a saturation curve. 
     
     
       4. The device of claim 1, further comprising an input amplifier and an indicator instrument, wherein said input amplifier is a part of said circuitry means and comprises means for receiving said output signal of said light-sensitive means, suppressing a continuous component of said output signal, and transmitting an intermittent component of said output signal to said indicator instrument. 
     
     
       5. The device of claim 1, wherein said circuitry means comprises a rating amplifier and first and second switch relays, said rating amplifier having an input receiving said output signal of said light-sensitive means and two output channels, said first and second switch relays being driven respectively by said two output channels of said rating amplifier, said first and second switch relays being set to different threshold values of energizing current. 
     
     
       6. The device of claim 5, further comprising washing means for washing said transparent element, said circuitry means further comprising first and second pulse generators, wherein said first switch relay, in an energized condition, activates said first pulse generator, said first pulse generator activates with each pulse said second pulse generator, and said second pulse generator energizes with each pulse said washing means. 
     
     
       7. The device of claim 6, further comprising an alarm installation connected to said output of said circuitry means for indicating the presence of ice on said transparent element, and wherein said circuitry means further comprises third and fourth relays, the contacts of which are closed in a non-energized condition, said third relay being located in said circuitry means between said first switch relay and said first generator, said fourth relay being located in said circuitry means between said second switch relay and said alarm installation, the windings of said third relay being connected to the output of said second switch relay, and the windings of said fourth relay being connected to the output of said first generator. 
     
     
       8. The device of claim 7, wherein said first pulse generator comprises delaying means for delaying the outputting of the pulses from said first pulse generator after activation of said first pulse generator for a time period longer than the time period between the energization of one and the other of said first and second switch relays when said transparent element is icing up.